Marxist Criticism treats literature as the product of social and economic pressures. Marxists believe that literature tends to reflect the ideology of the socioeconomic class in (or sometimes for) which it was produced.
Associate the following terms with traditional Marxism:
1. Base & superstructure
2. Class; proletariat; means of production
3. Bourgeois
4. (Capitalist) imperialism
5. Dialectical materialism
Major writers include:
Karl Marx; Friedrich Engels; Georg Lukacs; Walter Benjamin; Raymond Williams; Frederic Jameson.
Marxism influenced the later New Historicism & Sociological Criticism as well as Identity Criticism in that they all treat literature as primarily the product of external, historical forces.
For more information, I recommend Culler's Literary Theory: A Very Short Introduction.